Tunnel junction and charge perpendicular-to-plane magnetic recording sensors and method of manufacture

ABSTRACT

Magnetic tunnel junction (MTJ) and charge perpendicular-to-plane (CPP) magnetic sensors are disclosed which have a first antiferromagnetic layer for pinning the magnetization direction in a pinned layer and a second antiferromagnetic layer for providing bias stabilization of a free layer. The two antiferromagnetic layers may be formed from the same material and using a spin-flop effect may be initialized simulataneously. A disk drive using these sensors is disclosed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to sensors which can be used in adisk drive for magnetic read back and a manufacturing method thereof.

[0003] 2. Description of the Background Art

[0004] Magnetic sensors in many applications are required to have veryhigh sensitivity. One major example is the use of magnetic read backsensors in disk drives. As the density of recorded information increaseswith each succeeding product the required sensitivity of the sensor mustalso increase. Two classes of sensors having very high sensitivity arethe magnetic tunnel junction sensor (MTJ) and the chargeperpendicular-to-plane sensor (CPP). These sensors both depend onutilizing spin dependent electron movement through a thin nonmagneticseparation layer. On one side of the separation layer is a ferromagneticlayer, called the pinned layer, in which the direction of magnetizationis fixed. On the other side of the separation layer is a ferromagneticlayer, called the free layer, in which the direction of themagnetization is free to respond to an applied field. In a disk drivethe applied field is from a previously written transition on a disk. Inother applications the applied field could come from the position of anexternal magnet or from the change in location of the sensor relative toa field.

[0005] In disk drive applications, it is desirable to achieve maximumsensitivity and linearity. To achieve maximum linearity it is desirablefor the magnetization in the free layer in the absence of an externalfield be substantially parallel with the direction of the recordedtrack. It is also desirable for the magnetization of the pinned layer tobe perpendicular to the magnetization of the free layer in the absenceof an applied field. Accordingly it is desired that the magnetization inthe pinned layer be substantially perpendicular to the direction of therecorded track.

[0006] Another requirement for the free layer is that there belongitudinal magnetic bias stabilization. Imposing a preferredmagnetization direction in the free layer along the axis of the freelayer parallel to the recording medium and perpendicular to thedirection of the track insures good linearity and provides robustness todeleterious effects such as Barkhausen noise.

[0007] A common method of providing for the pinning of the pinned layeris to place a layer of antiferromagnetic material (AFM) adjacent to thepinned layer. At some point in the manufacture of the head, thestructure is heated above the blocking temperature of the AFM and thedevice is placed in an external magnetic field which is perpendicular tothe eventual direction of the recorded track. The blocking temperatureof an AFM material is the temperature above which the material no longerhas any exchange coupling strength. The sensor is then cooled in thepresence of the field. The applied field will orient the pinned layer inthe proper direction and as the AFM cools below the blockingtemperature, exchange coupling will maintain the orientation of themagnetization in the pinned layer. For the pinned layer this is thepinning process. This process is also called setting the AFM.

[0008] A known method for longitudinal biasing of the free layer is toprovide two hard magnets, one on each side of a portion of the freelayer. This is referred to as hard biasing. It is generally desirable toelectrically insulate the hard bias material from the layers comprisingthe active sensor. During the manufacture of the sensor, the directionof the magnetization in the hard magnet must be set by placing thesensors in a large magnetic field causing permanent alignment of thedirection of magnetization. The requirement of insulating the hard biasmagnets is a detractor for this approach.

[0009] A preferred method of providing longitudinal bias for the freelayer is to use another AFM layer and rely on exchange coupling. Theprinciple difficulty with this approach is that the direction ofmagnetization in the free layer must be substantially perpendicular tothe direction of magnetization in the pinned layer. Thus the steps ofheating and subsequent cooling in a field would be appropriate for oneof the AFM layers, but not the other. It is known to use two differentAFM materials which have two distinctly different blocking temperatures.The AFM layer with the highest blocking temperature is set first. Thenthe field angle is rotated 90° and the second AFM layer is set at alower temperature. There is generally one optimum AFM material whichwould serve for both the pinned layer and longitudinal stabilization ofthe free layer. However because of the requirement to have AFM materialswith different blocking temperatures, the optimum choice of AFMmaterials has been compromised. What is needed is a sensor structure anda method of manufacturing the sensor which allows for the use of two AFMlayers which can be set without compromising other aspects of thesensor.

SUMMARY OF THE INVENTION

[0010] The invention is an improved design and method of manufacturingof magnetic sensors which have the sense current substantiallyperpendicular to the direction of the layers in the sensor. Thesesensors use an antiparallel pinned substructure for the pinned layer orthe bias stabilization of the free layer. In all cases there are twoantiferromagnetic layers: one for setting the direction of magnetizationof the pinned layer and the other for use in the bias stabilization ofthe free layer. These AFM layers may be formed from the same material.Both AFM layers are simultaneously initialized in the same procedureutilizing a spin-flop effect.

[0011] For a fuller understanding of the nature and advantages of thepresent invention, reference should be made to the following detaileddescription taken together with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows a general view of MTJ and CPP sensors.

[0013]FIG. 2 shows a view of a sensor as constructed on a slider.

[0014]FIG. 3a shows a view of the layers in a sensor which has a pinnedlayer comprising an antiparallel pinned substructure and a trackwidthdefined by forming a nonmagnetic layer over a portion of the free layer.

[0015]FIG. 3b shows a view of the layers in a sensor which has bias tabscomprising an antiparallel pinned substructure and a trackwidth definedby forming a nonmagnetic layer over a portion of the free layer.

[0016]FIG. 4a shows a view of the layers in a sensor which has a pinnedlayer comprising an antiparallel pinned substructure and a magnetictrackwidth approximately equal to the width of the barrier layer.

[0017]FIG. 4b shows a view of the layers in a sensor which has bias tabscomprising an antiparallel pinned substructure and a magnetic trackwidthapproximately equal to the width of the barrier layer.

[0018]FIG. 5 shows a view of the layers in a sensor which has a pinnedlayer comprising an antiparallel pinned substructure and a biasstabilization AFM layer on the same side of the free layer as the pinnedlayer.

[0019]FIG. 6a shows a view of the layers in a sensor which has a pinnedlayer comprising an antiparallel pinned substructure and wherein thelayers all have comparable widths.

[0020]FIG. 6b shows a view of the layers in a sensor which has biasstabilization layers comprising an antiparallel pinned substructure andwherein the layers all have comparable widths.

[0021]FIG. 7a shows a view of the layers in a sensor which has a pinnedlayer comprising an antiparallel pinned substructure, the layers havecomparable widths, and the bias stabilization is provided by separatingan AFM layer from the free layer by a nonmagnetic layer.

[0022]FIG. 7b shows a view of the layers in a sensor in which the freelayer is an AP pinned substructure.

[0023]FIG. 8a shows the direction of magnetization in the layers of thesensor in the presence of a high magnetic field.

[0024]FIG. 8b shows the direction of magnetization in the layers of thesensor in the presence of a medium magnetic field.

[0025]FIG. 8c shows the direction of magnetization in the layers of thesensor in the presence of the optimum magnetic field.

[0026]FIG. 8d shows the angle of the direction of magnetization in theferromagnetic layer adjacent to the AFM layer for one specificantiparallel pinned substructure.

[0027]FIG. 9a shows a cross sectional view of a disk drive using thesensor of the present invention.

[0028]FIG. 9b show a top down view of a disk drive using the sensor ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029]FIG. 1 shows a diagram of some of the features of all of thesensor structures described herein. In FIG. 1 there is a gap 107 betweentwo metallic layers 101 and 102. Commonly the metallic layers 101 and102 are the electrical leads to the sensor. It is also possible in someembodiments for the layers 101, 102 to also serve as magnetic shieldsfor the sensor. The sensor comprises a pinned layer 103, a nonmagneticseparation layer 104, and a free layer 105. The pinned layer and thefree layer require magnetic stabilization layers which are not shown inFIG. 1. The width 108 of the sensor, specifically the active portion ofthe free layer, approximately defines the magnetic trackwidth in aapplication such as a disk drive. Outside of the sensor location the gapis filled with an insulating material 106. In all cases the direction ofthe sense current 107 is perpendicular to the layers in the sensor. In atypical mode of operation sense current 107 is passed through the sensorand the change in voltage resulting in a change in sensor resistance ismonitored. The principle difference between MTJ and CPP sensors is thatthe nonmagnetic separation layer 104 in a MTJ sensor is a thin insulatorand in a CPP sensor is a thin conductor. The nonmagnetic separationlayer in a MTJ sensor is sometimes called a barrier layer. MTJ sensorstend to be higher impedance devices compared to CPP sensors. Bothsensors depend on modulating the spin-dependent movement of electronsacross the nonmagnetic separation layer by changing the direction of themagnetization in the free layer in response to an external appliedmagnetic field. For the purposes of this invention it is immaterialwhether the current direction 107 is from bottom to top as shown in FIG.1 or from top to bottom. It is also immaterial whether the pinned layer103 is on the bottom of the gap as shown in FIG. 1 or on the top of thegap. For clarity all the structures are drawn with the pinned layer onthe bottom.

[0030] For disk drive applications the view of the sensor in FIG. 1 isof the sensor as presented to the disk. The sensor is ordinarilyconstructed on a slider as illustrated in FIG. 2. In FIG. 2 the sensor202 is constructed on the trailing surface 204 of a slider 201. Metallicpads 203 are provided to make electrical connections with the sensor.These sensors are read-only elements. There is a write head also placedon the slider for recording information to the disk.

[0031] Several specific examples of sensors will now be discussed. Allof these sensors have several common attributes:

[0032] 1) The sense current is perpendicular to the plane of the layersof the sensor and flows from one lead across the gap through the sensorto the other lead.

[0033] 2) The nonmagnetic separation layer between the pinned layer andthe free layer is either an thin insulator layer such as alumina in thecase of the MTJ sensor or a thin metal layer such as Cu in the case ofthe CPP sensor.

[0034] 3) All the sensors have at least one antiparallel pinned (APpinned) substructure. The AP pinned substructure can serve as the pinnedlayer of the sensor or as a portion of the bias tabs for the free layer.In one embodiment the AP pinned substructure comprises the free layer.

[0035] 4) All the sensors have two separate substantially planarantiferromagnetic (AFM) layers. One is used to stabilize the pinnedlayer and the other is used to assist in the longitudinal stabilizationof the free layer. In accordance with this invention, the two AFM layerscan be constructed of substantially the same material.

[0036] 5) In all cases the two AFM layers can be set during the sameinitialization procedure in accordance with this invention.

[0037] Certain of the layers common to the embodiments discussed belowhave similar compositions. The ferromagnetic free layer and theferromagnetic portion of the pinned layers are usually made of alloys ofNiFe, CoFe, or CoNiFe. The nonmagnetic layer between the twoferromagnetic layers in an AP pinned configuration is commonly Ru butcan also be made from other materials such as Ta. Copper is also used asa nonmagnetic conductor. The AFM materials can be made from materialscontaining Mn such as PtMn, NiMn, FeMn and IrMn. The AFM material canalso be made from materials which do not contain Mn such as combinationsof NiO or CoNiO.

[0038]FIG. 3a shows one preferred embodiment of a sensor in more detail.Additional layers to promote adhesion, control film growth, enhancesensitivity, or control film surface smoothness may also be present. Afirst AFM layer 301 is deposited on a lead 302. Two ferromagnetic layers303, 304 are deposited on the first AFM layer 301. The two ferromagneticlayers 303, 304 are separated by a nonmagnetic layer 305. The twoferromagnetic layers 303 and 304 together with the nonmagnetic layer 305comprise the AP pinned substructure 340. This AP pinned substructure 340serves as the pinned layer for this sensor. In the absence of anexternal field the direction of magnetization 316 in the firstferromagnetic layer 303 is approximately opposite to the direction ofmagnetization 317 of the second ferromagnetic layer 304. The next layeris the nonmagnetic separation layer 306. The free layer 307 is depositedon the nonmagnetic separation layer 306. In the absence of an externalmagnetic field the direction of magnetization 318 in the free layer 307is substantially parallel to the recording medium and perpendicular tothe magnetizations 316, 317 in the AP pinned substructure 340. The layerbetween the free layer 307 and the lead 308 has two portions. Oneportion 309 comprises an nonmagnetic metal. This portion 309 could alsobe an insulator. This nonmagnetic portion 309 defines the active portionof the free layer 307 and therefore the magnetic trackwidth when thesensor is used in a disk drive. The other portion is a second AFM layer310. This layer provides magnetic bias stabilization for the free layer307. The portion of the free layer 307 in direct contact with the AFMlayer 310 is substantially inactive for sensing an external field.Except for the second AFM layer 310 and the nonmagnetic layer 309, thewidths of the layers are typically wider than the magnetic track(determined by the active portion of the free layer). The gap beyond thelocation of the sensor layers is filled with an insulating material 311.

[0039] The structure shown in FIG. 3b is similar to that illustrated inFIG. 3a in that the physical width of the pinned and free layers arewider than the magnetic track width. A first AFM layer 301 is depositedon the bottom lead 302. A single ferromagnetic pinned layer 312 isdeposited on the first AFM layer 301. The nonmagnetic separation layer306 is formed between the pinned layer 312 and the free layer 307. Theactive region of the free layer is defined by covering a portion of thefree layer with a nonmagnetic metal or insulating layer 315. The otherportion of the free layer is covered with a AP pinned substructure 350comprising a thin nonmagnetic layer 313, a ferromagnetic layer 314, anda portion of the free layer 307. In this configuration the direction ofmagnetization 320 in the ferromagnetic layer 314 is controlled with asecond AFM layer 310. The magnetization 321 in the portion of the freelayer 307 adjacent to the ferromagnetic layer 314 and the nonmagneticlayer 313 is pinned opposite to the magnetization 320 in theferromagnetic layer 314 thus providing magnetic bias stabilization inthe active portion of the free layer. The upper lead 308 is placed onthe second AFM layer 310.

[0040] In FIG. 3a the AP pinned substructure 340 is comprised in thepinned layer. In FIG. 3b the AP pinned substructure 350 is comprised inthe free layer bias stabilization layers. These latter layers comprisinga nonmagnetic metal 313, a ferromagnetic layer 314 and an AFM layer 310are sometimes referred to as bias tabs 360. One minor disadvantage ofthe structures in FIG. 3 is that the sense current flows both in theactive and inactive portion of the sensor. This current shunting has thepractical effect of reducing the overall sensitivity of the sensor. Anembodiment which does not have this disadvantage is shown in FIGS. 4a,b.

[0041] The embodiment shown in FIG. 4a has a first AFM layer 402deposited on a lead 401. An AP pinned substructure 440 comprising twoferromagnetic layers 403, 405 separated by a nonmagnetic layer 404 isconstructed on the first AFM layer 402. The free layer 407 is separatedfrom the pinned layer by the nonmagnetic separation layer 406. A portionof the free layer is covered by a nonmagnetic metal or insulating layer409. Another portion of the free layer is covered by a second AFM layer408. The second AFM layer 408 is adjacent to a lead 415. As was the casein FIGS. 3a,b the remaining portion of the gap is filled with aninsulating material 410. In this embodiment the magnetic trackwidth isapproximately defined by the width of the pinned layer comprising inthis case the layers in the AP pinned substructure 440. The shuntingcurrent is greatly reduced compared to the sensors illustrated in FIG.3a,b.

[0042] An alternative embodiment is shown in FIG. 4b. In this case thepinned layer 411 is a single layer. The free layer 407 is separated fromthe pinned layer 411 by a nonmagnetic separation layer 406. The APpinned substructure 450 comprises a portion of the free layer 407, anonmagnetic layer 412, and a ferromagnetic layer 413. The bias tabs 460comprise a nonmagnetic layer 412, a ferromagnetic layer 413 and the AFMlayer 414. The AFM layer 414 controls the direction of magnetization inthe ferromagnetic layer 413. A lead 415 is placed on the second AFMlayer 414. The width of the pinned layer 411 is approximately equal tothe desired magnetic trackwidth. As was the case for the structure shownin FIG. 4a, the shunting current is minimized.

[0043] One of the disadvantages of the sensor structure shown in FIGS.4a,b is that the width of the portion of the free layer covered by thenonmagnetic metal 409 is preferably equal to the width of thenonmagnetic separation layer 406 and the pinned layer below thenonmagnetic separation layer. It is also desirable that the nonmagneticmetal 409 is aligned with the barrier layer 406. An embodiment whichdoes not have this alignment constraint is illustrated in FIG. 5.

[0044] In FIG. 5 the first AFM layer 502 is placed on a lead 501. Thesensor pinned layer is an AP pinned substructure 530 comprising twoferromagnetic layers 503, 504 separated by a nonmagnetic layer 505. Thefree layer 508 is separated from the pinned layer by the nonmagneticseparation layer 506. The second AFM layer 507 providing magnetic biasstabilization for the free layer 508 is on the same side of the freelayer as the nonmagnetic separation layer 506. This reduces thealignment requirements associated with the sensor illustrated in FIGS.4a,b. In FIG. 5 it is desirable to insulate the second AFM layer 507from the rest of the sensor stack. This is most conveniently done byusing the insulating material in the remainder of the gap 511 in thevicinity 512 near the barrier layer. It is also desirable for the leadmaterial 513 which is adjacent to the free layer 508 to be nonmagnetic.A variation on this embodiment is to use a single ferromagnetic layerfor the sensor pinned layer and bias exchange tabs comprising an APpinned substructure for free layer bias stabilization wherein the biastabs are on the same side of the free layer as the barrier layer.

[0045] Significant processing simplicity is achieved when all of thelayers comprising the sensor stack are the same width. Alignmentrequirements are greatly reduced when all the layers are approximatelyequal to the desired trackwidth. FIGS. 6a,b and FIGS. 7a,b showembodiments of sensors where all the layers in the sensor stack are ofsubstantially the same width. These configurations are sometimes calledin-stack biasing schemes. One feature which the in-stack biasing schemeshave in common is that using the invention disclosed wherein the entiresensor can be constructed without breaking the vacuum. For conventionalsensors part of the sensor would be constructed, then the partlycompleted sensor would be removed from the vacuum systems used forfabrication for initialization of one of the AFM layers, then thensensor would be returned to the vacuum system for completion. Thespin-flop method of initialization allows the complete sensor to befabricated and then the initialization is accomplished with a singleprocedure.

[0046]FIG. 6a shows a first AFM layer 602 deposited on a lead 601. Thesensor pinned layer is an AP pinned substructure 630 comprising twoferromagnetic layers 603, 605 separated by a nonmagnetic layer 604. Anonmagnetic separation layer 606 separates the free layer 607 from thepinned layer. The magnetic bias stabilization of the free layer 607 isprovided by a ferromagnetic layer 609 weakly coupled to the free layer607 with a nonmagnetic conducting layer 608. It is desireable that thefree layer 607, nonmagnetic layer 608 and ferromagnetic layer 609combination not exhibit significant spin-valve behavior. For this reasontantalum or ruthenium is convenient to use for the nonmagnetic layer608. The direction of magnetization 618 in the ferromagnetic layer 609is controlled by a second AFM layer 610. The direction of magnetization618 is substantially perpendicular to the direction of magnetizations621,622 in the AP pinned substructure 630. The second AFM layer 610 isadjacent to a lead 617. The areas 611 in the gap outside the sensor isfilled with an insulating material.

[0047]FIG. 6b illustrates an alternative embodiment. In FIG. 6b a firstAFM layer 602 is deposited on a lead 601. A single ferromagnetic layer612 is deposited on the first AFM layer and serves as the pinned layerof the sensor. A nonmagnetic separation layer 606 is formed between thepinned layer 612 and the free layer 607. The next layer 613 is anonmagnetic conductor which separates the biasing layers 640 from thefree layer 607. The biasing layers 640 can be considered as a singlebiasing tab. Two ferromagnetic layers 614, 616 separated by anonmagnetic layer 615 comprise the AP pinned substructure 650 of thebias tab 640. The second AFM layer 610 is located between the AP pinnedsubstructure 650 and a lead 617.

[0048] Another embodiment is shown in FIG. 7a. A first AFM layer 701 isdeposited on a lead 702. The sensor pinned layer is an AP pinnedsubstructure 720 comprising two ferromagnetic layers 703, 705 separatedby a nonmagnetic layer 704. The AP pinned substructure 720 is placed onthe first AFM layer 701. A nonmagnetic separation layer 706 separatesthe free layer 707 from the AP pinned substructure 720. A layer ofcopper or other nonmagnetic conductor 708 is then deposited on the freelayer 707 and a second AFM layer 709 is placed on the layer 708. Tocomplete the sensor, a lead 710 is placed on the second AFM layer 709.The other space in the gap is filled with an insulator 711. This is anunusual sensor in that AFM material is generally thought to offer onlysurface exchange coupling. As such it is unexpected that the second AFMlayer 709 is effective in stabilizing the free layer 707 through the Culayer 708. A thickness of copper which is effective is roughly from 1 to2 nm. More information on the physics related to this behavior can befound in N. J. Gokenmeijer, et al, Phys. Rev. Lett. 79, 4270 (1997).

[0049]FIG. 7b shows an alternative embodiment. In FIG. 7b the first AFMlayer 701 is formed on a first lead 702. A single ferromagnetic layer715 serves as the sensor pinned layer. A nonmagnetic separation layer706 separates the pinned layer 715 from the free layer. In FIG. 7b thefree layer is comprised of an AP pinned substructure. This AP pinnedsubstructure is comprised of a ferromagnetic layer 716 adjacent to thenonmagnetic separation layer 706, a nonmagnetic layer 717, and anotherferromagnetic layer 718. The upper ferromagnetic layer 718 of the APpinned substructure 721 is weakly coupled to a second AFM layer 709through a conductor layer 708. Another lead 710 is then formed over theAFM layer 709. The other portions of the gap is filled with aninsulating material 711. The sensor in FIG. 7b is unusual in that an APpinned substructure is used as the free layer. This arrangement has theadvantage that the net magnetic moment of the free layer may besignificantly reduced compared with using a single ferromagnetic layer.

[0050] The present invention allows the use of the same AFM material tobe used for setting both the pinned layer and the bias stabilization ofthe free layer. Thus the material may be chosen for optimal magneticperformance. The key feature in being able to use the same AFM materialis to be able to initialize the layers given the same blockingtemperature. The initialization process makes use of magnetic behaviorgenerally referred to as a spin flop effect.

[0051] The use of the spin-flop effect to initialize a sensor isillustrated in FIG. 8a-d. The sensor shown in exploded form in FIG. 8a-cis the same sensor illustrated in FIG. 6a. Although the specific examplediscussed in FIGS. 8a,b,c,d is shown in detail for the sensor in FIG.6a., the use of the spin-flop effect can be used on any of the sensorsdescribed above. In FIG. 8a the important magnetic layers in the sensorare shown including the first AFM exchange layer 806 adjacent to a firstferromagnetic layer 805, a second ferromagnetic layer 804, the freelayer 803, a third ferromagnetic layer 802, and the AFM layer 801adjacent to the third ferromagnetic layer 802. Also, the magnetizationdirections 807, 808, 809, 810 are shown. For clarity, the additionalnonmagnetic layers are not shown. FIG. 8a shows the directions ofmagnetization 807, 808, 809, 810 when the structure has been placed inan external high magnetic field. The direction of the field is indicated812. The bias stabilization layer 802 and the free layer 803 are weaklycoupled for this particular sensor configuration. When the temperatureof the AFM exceeds the blocking temperature, the magnetization of thebias stabilization layer 807 and the free layer 808 align with theapplied external field 812 for high values of the applied field. Forhigh values of the applied field the antiparallel coupling between thefirst ferromagnetic layer 805 and the second ferromagnetic layer 804comprising the AP pinned layer 811 is broken and the magnetization ofboth the first ferromagnetic layer 810 and the second ferromagneticlayer 809 align with the applied field. This magnitude of field is notuseful for initialization. As the applied field is reduced, thedirection of the magnetizations 810, 809 in the pinned layer 811 willbegin to rotate in order to seek the lowest energy. FIG. 8b shows thecase where the magnetizations in the AP pinned substructure have begunto rotate as the magnitude of the applied field 812 is reduced. Themagnetizations 810, 809 rotate away from the direction of the appliedfield 812 and in opposite directions from each other. This behavior isthe spin-flop effect. More specific details of the physics related tothe spin-flop effect may be found in Beach, et al., “AP-pinned spinvalve GMR and magnetization” J. Appl. Phys. 87, p.5723 (2000).

[0052]FIG. 8c shows that at some optimum value of the applied field 812the magnetization of the first ferromagnetic layer 805 will beperpendicular to the applied external field 812 and perpendicular to themagnetization 807 of the bias stabilization layer 802 which is stillaligned with the applied field 812. This is the value of the appliedfield which is used when cooling both AFM layers 806, 801 below theblocking temperature to achieve initialization. At the optimum externalfield value the direction of the magnetization 809 in the secondferromagnetic layer 804 need not be opposite from the magnetization 810of the first ferromagnetic layer 805. However when the external field isremoved, the magnetization 809 of the second ferromagnetic layer 804will be substantially opposite from the magnetization 810 of the firstferromagnetic layer 805. Without using the spin-flop effect to inducethe appropriate rotation of magnetization in an AP pinned substructureit is not practical to use the optimal choice of the same material forthe two AFM layers because of the difficulty with initialization.

[0053] The same spin-flop effect can be utilized in initializing all ofthe sensors discussed above. The common feature is that there is atleast one AP pinned substructure in each of the sensors. The onlydifferences is in what direction to apply the external magnetic fieldand what magnitude of the external field to use. The direction of theexternal field used for initialization depends on where the AP pinnedsubstructure is located in the sensor. In FIG. 3a the direction of theapplied field 330 is perpendicular to the desired direction of themagnetization 316 in the ferromagnetic layer 303 adjacent to the AFMlayer 301. In FIG. 3b the direction of the initialization field 331 isperpendicular to the direction of magnetization 320 in the ferromagneticlayer 314 adjacent to the AFM 310. In FIG. 4a the direction of theapplied field 430 is perpendicular to the desired direction of themagnetization 420 in the ferromagnetic layer 403 adjacent to the AFMlayer 402. In FIG. 4b the direction of the initialization field 431 isperpendicular to the direction of magnetization 421 in the ferromagneticlayer 413 adjacent to the AFM layer 414. In FIG. 5 the direction of theapplied field 530 is perpendicular to the desired direction of themagnetization 520 in the ferromagnetic layer 503 adjacent to the AFMlayer 502. In FIG. 6a the direction of the applied field 660 isperpendicular to the desired direction of the magnetization 622 in theferromagnetic layer 603 adjacent to the AFM layer 602. In FIG. 6b thedirection of the applied field 661 is perpendicular to the desireddirection of the magnetization 623 in the ferromagnetic layer 616adjacent to the AFM layer 610. In FIG. 7a the direction of the appliedfield 730 is perpendicular to the desired direction of the magnetization732 in the ferromagnetic layer 703 adjacent to the AFM layer 701. InFIG. 7b the direction of the applied field 733 is perpendicular to thedesired direction of the magnetization 731 in the ferromagnetic layer718. As a general rule the direction of the initialization field isperpendicular to the direction of the magnetization of the ferromagneticportion of the APP substructure which is exchange coupled to an AFMlayer.

[0054] After the direction of the external magnetic field has beendetermined the magnitude must be chosen. FIG. 8d shows an example of theangle of the magnetization 810 in the first ferromagnetic layer 805 inthe pinned layer 811 as a function of field magnitude. In FIG. 8d theangle is measured from the desired direction of the final angle. Thetargeted angle is 90° with respect to the field direction. Therefore thedesired angle as shown in FIG. 8d is 0°. For this specific case, thecoupling strength across the nonmagnetic layer is 0.5 erg/cm², and themoments/area of the first and second ferromagnetic layers are 0.2 and0.4 memu/cm², respectively. The optimum field strength to achieve thespin-flop effect is approximately 2200 Oe for this specific example.Other structures with different materials, thicknesses, and momentswould have a different optimal external field strength. Therefore thevalue of the optimal external field strength is somewhat different foreach particular sensor. The optimal value of external field magnitude isalso influenced to a small extent by process variations in the filmlayer properties. For this reason the optimum value is usuallydetermined by first performing a process tolerance study using aspecific sensor.

[0055] As a practical matter, better process consistency is achieved byfirst increasing the applied field to a high value and then reducing themagnitude until the optimum value is applied. However it is alsopossible to place the sensor directly into a field having the optimumvalue or to raise the field from an initial value of zero.

[0056]FIGS. 9a and 9 b show the present invention as used in a magneticrecording disk drive. The magnetic recording disk 902 is rotated bydrive motor 904 with hub 906, which is attached to the drive motor. Thedisk comprises a substrate, a magnetic layer, an optional overcoat layersuch as carbon, and typically a lubricant layer such as aperfluoropolyether. The substrate is typically either aluminum, glass,or plastic. Some disk drives are designed such that the slider 910 comesto rest on the disk when the disk drive is stopped. In other diskdrives, the slider is lifted off of the disk surface when the disk driveis turned off. The latter is preferable when the surfaces of the sliderand the disk are designed to have very low roughness. This isadvantageous for designs requiring frequent or continuous contactbetween the slider and the disk during normal operation.

[0057] A recording head assembly 908 is formed on the trailing surfaceof a slider 910. The slider has a trailing vertical surface 909. Therecording head assembly usually comprises a separate write element alongwith the read sensor. The slider 910 is connected to the actuator 912 bymeans of a rigid arm 914 and a suspension 916. The suspension 916provides a force which pushes the slider toward the surface of therecording disk 902.

[0058] An important use of these sensors is in disk drives. Anotherapplications of these sensors can be the use in static memory storagedevices and other devices requiring very high sensitivity.

[0059] While the invention has been described above in connection withpreferred embodiments thereof and as illustrated by the drawings, thosewith skill in the art will readily recognize alternative embodiments ofthe invention can be easily produced which do not depart from the spiritand scope of the invention as defined in the following claims.

We claim:
 1. A magnetic sensor for use with sense current appliedsubstantially perpendicular to the plane of the layers in the sensor,comprising: a first antiferromagnetic layer; a pinned layer comprisingan antiparallel pinned substructure formed on said firstantiferromagnetic layer, said antiparallel pinned substructurecomprising a first ferromagnetic layer, a nonmagnetic layer formed onsaid first ferromagnetic layer, and a second ferromagnetic layer formedon said nonmagnetic layer, wherein said first ferromagnetic layer isexchanged coupled to said first antiferromagnetic layer; a nonmagneticseparation layer formed on said second ferromagnetic layer of saidantiparallel pinned substructure; a ferromagnetic free layer formed onsaid nonmagnetic separation layer; and, a second antiferromagnetic layersupporting magnetic bias stabilization of said ferromagnetic free layer.2. A magnetic sensor as in claim 1 wherein said first and secondantiferromagnetic layers are made of the same material havingsubstantially the same blocking temperature.
 3. A magnetic sensor as inclaim 2 wherein said nonmagnetic separation layer is formed from aconductive material.
 4. A magnetic sensor as in claim 2 wherein thenonmagnetic separation layer is formed from an insulating material.
 5. Amagnetic sensor for use with sense current applied substantiallyperpendicular to the plane of the layers in the sensor, comprising: afirst antiferromagnetic layer; a pinned first ferromagnetic layer formedon said first anti ferromagnetic layer; a first nonmagnetic separationlayer formed on said pinned first ferromagnetic layer; a free secondferromagnetic layer formed on said nonmagnetic separation layer; anantiparallel pinned substructure coupled to said free layer, comprisinga third ferromagnetic layer; and, a second antiferromagnetic layerexchange coupled with said third ferromagnetic layer.
 6. A magneticsensor as in claim 5 wherein said antiparallel pinned substructure iscoupled to said free ferromagnetic layer through a second nonmagneticseparation layer.
 7. A magnetic sensor as in claim 5 wherein saidantiparallel pinned substructure is coupled to a portion of said freeferromagnetic layer.
 8. A magnetic sensor as in claim 5 wherein saidfirst and second antiferromagnetic layers are made of the same materialhaving substantially the same blocking temperature.
 9. A magnetic sensoras in claim 5 wherein said first nonmagnetic separation layer is formedfrom a conductive material.
 10. A magnetic sensor as in claim 5 whereinsaid first nonmagnetic separation layer is formed from an insulatingmaterial.
 11. A magnetic sensor for use with sense current appliedsubstantially perpendicular to the plane of the layers in the sensor,comprising: a first antiferromagnetic layer; a pinned firstferromagnetic layer formed on said first antiferromagnetic layer; afirst nonmagnetic separation layer formed on said pinned firstferromagnetic layer; a free layer formed on said first nonmagneticseparation layer, said free layer comprising an antiparallel pinnedsubstructure; a second nonmagnetic separation layer formed on said freelayer, and; a second antiferromagnetic layer formed on secondnonmagnetic separation layer.
 12. A magnetic sensor as in claim 11wherein said first nonmagnetic separation layer is formed from aconductive material.
 13. A magnetic sensor as in claim 11 wherein saidfirst nonmagnetic separation layer is formed from an insulatingmaterial.
 14. A method of simultaneously initializing twoantiferromagnetic layers in a magnetic sensor having an AP pinnedsubstructure comprising a first ferromagnetic layer, a firstantiferromagnetic layer exchange coupled to said first ferromagneticlayer and a second antiferromagnetic layer supporting magnetic biasstabilization of the free layer, said magnetic sensor for use with sensecurrent applied substantially perpendicular to the plane of the layersin the sensor, comprising: placing the sensor in an external magneticfield; adjusting the magnitude of said magnetic field to cause themagnetization of said first ferromagnetic layer in said AP pinnedsubstructure to be substantially perpendicular to the external magneticfield direction; heating the sensor above the blocking temperature ofboth said first and second antiferromagnetic layers; and, cooling thesensor below the blocking temperature of both the first and secondantiferromagnetic layer in the presence of said external magnetic field.15. A method of simultaneously initializing the antiferromagnetic layersin a magnetic sensor which has a first antiferromagnetic layer exchangedcoupled to a pinned layer and a second antiferromagnetic layer exchangedcoupled to a ferromagnetic layer, said ferromagnetic layer comprising aportion of an AP pinned substructure supporting magnetic biasstabilization of a free layer, said magnetic sensor for use with sensecurrent applied substantially perpendicular to the plane of the layersin the sensor, comprising: placing the sensor in an external magneticfield; adjusting the magnitude of said external magnetic field to causethe magnetization of said ferromagnetic layer in said antiparallelpinned substructure to be substantially perpendicular to the externalmagnetic field direction; heating the sensor above the blockingtemperature of both said first and second antiferromagnetic layers; and,cooling the sensor below the blocking temperature of both the first andsecond antiferromagnetic layer in the presence of said external magneticfield.
 16. A magnetic storage system, comprising: a magnetic storagemedium for the recording of data; a motor connected with said magneticstorage medium; a slider having a magnetic recording head assemblymaintained in close proximity to the storage medium during relativemotion between said head assembly and said storage medium, saidrecording head assembly having a magnetic sensor comprising, a firstantiferromagnetic layer; a pinned layer formed on said firstantiferromagnetic layer, wherein said pinned layer comprises an APpinned substructure; a nonmagnetic separation layer formed on saidpinned layer; a free layer formed on said nonmagnetic separation layer;a second antiferromagnetic layer supporting bias stabilization of saidfree layer; and, a suspension connected to said slider which positionssaid slider for magnetic recording on the disk; wherein said first andsecond antiferromagnetic layers are made of the same material havingsubstantially the same composition and having substantially the sameblocking temperature.
 17. A magnetic storage system as in claim 16wherein said nonmagnetic separation layer is formed from a conductivematerial.
 18. A magnetic storage system as in claim 16 wherein saidnonmagnetic separation layer is formed from an insulating material. 19.A magnetic storage system, comprising: a magnetic storage medium for therecording of data; a motor connected to said magnetic storage medium; aslider having a magnetic recording head assembly maintained in closeproximity to the storage medium during relative motion between said headassembly and said storage medium, said recording head assembly having amagnetic sensor comprising, a first antiferromagnetic layer; aferromagnetic pinned layer exchange coupled to said firstantiferromagnetic layer; a nonmagnetic separation layer formed on saidpinned layer; a free second ferromagnetic layer formed on saidnonmagnetic separation layer; one or more bias tabs coupled to a portionof said free layer, said bias tabs comprising an AP pinned substructureexchange coupled to a second antiferromagnetic layer, said bias tabsproviding magnetic bias stabilization of said free layer, wherein saidfirst and second antiferromagnetic layers are made of the same materialhaving substantially the same composition and having substantially thesame blocking temperature; and, a suspension connected to the sliderwhich positions said slider for magnetic recording on the disk.
 20. Amagnetic storage system as in claim 19 wherein said nonmagneticseparation layer is formed from a conductive material.
 21. A magneticstorage system as in claim 19 wherein said nonmagnetic separation layeris formed from a insulating material.